Prior proposals for such applicators include providing for needle extension as a first stage in their use, i.e. having an as-supplied state with the needle retracted. Cartridges supplied pre-filled with a measured drug dose typically have fixed needles, in which case such first stage involves movement of the cartridge internally of the applicator. It is known for such movement to be by the same drive force as serves to discharge the cartridge contents through the needle by continuation of such force application through and after cartridge movement for needle extension. It is further known, in relation to typical cartridges having a piston for expression of contents, for drive force application to rely on force transmission through incompressible liquid contents of the cartridge to achieve the first needle extension stage of movement of the cartridge. Examples include EP0516473, which clearly accepts drug weepage through its needle during extension as an inevitability, and also our own earlier WO93/23098 and WO95/35126.